Thyroid Dysfunction In Metabolic Syndrome: a Case-Control Study

Abstract

Background: Metabolic syndrome (MetS) and thyroid dysfunction are prevalent endocrine disorders that mutually influence each other and synergistically increase cardiovascular morbidity and mortality. Aim: To compare serum free triiodothyronine (FT3), free thyroxine (FT4), and thyroid-stimulating hormone (TSH) levels between patients with MetS and coexisting thyroid disorder and healthy controls, and to quantify the clinical magnitude of these differences. Methods: In this hospital-based case–control study, 100 patients with MetS (NCEP ATP III criteria) and a confirmed coexisting thyroid disorder were compared with 100 age and sex-matched healthy controls. FT3, FT4, and TSH were measured by electrochemiluminescence immunoassay. Statistical comparisons used independent t-tests (or Mann– Whitney U when appropriate); effect sizes were calculated as Cohen’s d and eta squared (η²). Results: Compared with healthy controls, MetS patients with thyroid dysfunction had significantly lower mean FT3 (difference –0.34 pg/mL, p = 0.0025) and FT4 (difference –0.88 ng/dL, p = 0.04). TSH was markedly higher in cases (difference +26.58 µIU/mL, p < 0.0001), with a large effect size (Cohen’s d = 1.38) explaining 32.4% of the variance. However, the TSH elevation is largely explained by the inclusion criterion of pre-existing thyroid disorder. Conclusion: MetS with coexisting thyroid disorder is characterized by a distinct thyroid profile of low FT3/FT4 and markedly elevated TSH. The large effect size and substantial variance explained by TSH highlight its potential as a sensitive clinical biomarker. Study interpretations do not support routine TSH screening in all MetS patients but rather targeted testing in those with clinical features of hypothyroidism.